1. Field of the Invention
This invention relates to multicast packet routing.
2. Related Art
In a computer network, it is often desirable to transmit messages from a single source to a selected plurality of destinations. This activity is often referred to as "multicast routing." It is further desirable for the plurality of destinations to be capable of self-selection, so as to add themselves to, or to take themselves off, multicast distribution groups.
One method in the known art is the IGMP (Internet Group Management Protocol), in which messages are transmitted from a single source to a plurality of destinations, and in which destination devices can add themselves to, or take themselves off, multicast distribution groups. One problem with IGMP is that it uses bi-directional communication between routing devices (that receive messages from the source device) and the destination devices, so that routing devices intermediate between the source and destinations can determine how to route multicast messages. IGMP is not well suited when a primary communication path between the source and the destinations is unidirectional, such as in distribution systems using satellite communication.
Accordingly, it would be desirable to provide a method and system for multicast group routing using unidirectional links. This advantage is achieved in an embodiment of the invention in which a set of uplink routers and a set of downlink routers provide a unidirectional distribution path from a set of sources to a set of destinations, and in which some (but not all) downlink routers act as proxies for others to inform uplink routers whether distribution should occur over that unidirectional distribution path.